Positive displacement fluid measurement systems can be used to measure a fluid flow rate or volume. For example, dispensing systems can use feedback from a positive displacement fluid meter to control the volume of fluid dispensed. Such control systems can be used in lieu of time-on controls to more accurately dispense precise amounts of fluid.
One type of positive displacement fluid measurement system is a gear flow meter, e.g. an oval gear or lobe meter. A traditional oval gear meter provides a pair of oval gears positioned within an oval gear chamber such that the gears rotate in concert. A lobe meter, provides a pair of lobe elements within a chamber which interlock and rotate about respective axes. In each case, fluid enters the chamber through a fluid inlet and causes the gears to rotate, allowing fluid to pass around the gears to a fluid outlet within precisely measured pockets. In an oval gear meter, the pockets are defined between the rotating oval gears and the inner chamber wall. In a lobe meter, spaces between the lobes of provide the pockets. Ideally, in each case, none of the fluid being metered passes directly between the gears themselves, so that the volume of fluid exiting the chamber during each rotation is known. Thus the volume of fluid flow through a gear meter can be measured by measuring the number of rotations of the gears. Likewise flow rate can be determined from the speed with which the gears rotate.
For measuring the gear rotation, gear meters frequently include additional gears. For example, an oval gear meter can include timing gear systems located external of the chamber to translate the number of rotations of the oval gears into an appropriate signal. Oval gear and other positive displacement flow meters utilizing timing gear systems usually have a gear chamber that includes one or more shaft apertures for the shafts coupling the gears to the external timing gears. Using more recent developments, some gear meters instead use a non-contact sensor placed outside a substantially sealed chamber to determine gear movement within the chamber. For example, magnetic and optical sensors have been incorporated into gear flow meters to measure gear movement without the need for openings or apertures within the gear chamber.
Fluid flow gear meters are used in a variety of applications in which it is desirable to measure the flow of small volumes of fluids. Thus, gear meters can be exposed to different types of fluids, require different measurement capabilities, and be placed in different environmental conditions depending on the particular application. Gear meters may also employ one or more of a variety of measurement technologies. Accordingly, fluid flow meter design must account for a large number of changing conditions among different applications.